Can't output Float values to text file using Python 3

Question

My code currently produces an array (ra) containing only float values. If a value in this array meets a certain condition, I want to output that specific value to a text file. Here is the part of my code in question:

outputFile = open('outFile.txt', 'wb')
i = 0
membersOuter = []
membersInner = []
membersCore = []
while i < (len(ra)):
    DiffFinal = Diff[i] * 3600 * kpc_per_arcsec / 1000 #just converting values from an array called Diff
    if DiffFinal < 2.0:
        membersOuter.append(ra[i])
    if DiffFinal < 1.0:
        membersInner.append(ra[i])
    if DiffFinal < 0.5:
        membersCore.append(ra[i])
        outputFile.write(ra[i] + ' ') #this is the part causing problems
    i += 1

The code successfully creates arrays for the 3 member categories. However, I want to be able to output the ra values (which are all floats) meeting the final condition to outFile.txt. When I run this code I get the error:

TypeError: 'float' does not support the buffer interface

I am using Python 3.4, and searching past questions told me this process has changed since lower versions. Some changes that were recommended included:

outputFile.write(str(ra[i]))
TypeError: 'str' does not support the buffer interface

and

outputFile.write(bytes(ra[i]))
TypeError: 'float' object is not iterable

Answer 1

String formatting should help with both of your problems. Here is your example, with some irrelevant parts removed:

ra = [1.5, 2.1, 3.3, 11./7]

outputFile = open('outFile.txt', 'w')
for i in range(4):
    outputFile.write('{} \n'.format(ra[i]))

Notice:

• The output text file is open for text, not binary, w, not wb
• The float variable is formatted by the {} directive inside the string.
• The whitespace and newline are easily included in the format string.